A variety of different devices have been developed for absorbing the kinetic energy resulting from impact with a moving vehicle, and for the containment of forces exerted by soil or water. Highway barriers, for example, are intended to provide a continuous wall or barrier along the center line or shoulder of a highway when laid end-to-end to absorb grazing blows from moving vehicles. One commonly used highway barrier is formed of pre-cast reinforced concrete, and is known as the “Jersey” style barrier. Highway barriers of this type have a relatively wide base resting on the pavement or shoulder of the highway; opposed side walls and opposed end walls. The side walls consist of a “curb reveal” extending vertically upwardly from the base a short distance, a vertically extending top portion connected to the top wall of the barrier and an angled portion between the curb reveal and the vertical top portion. This design is intended to contact and redirect the wheels of a vehicle in a direction toward the lane of traffic in which the vehicle was originally traveling, instead of the lane of opposing traffic. See, for example, U.S. Pat. No. 4,059,362.
One problem with the Jersey-style highway barriers described above is the weight of reinforced concrete. A concrete barrier having a typical length of twelve feet weighs about 2,800-3,200 pounds, and requires special equipment to load, unload and handle on site. It has been estimated that for some road repairs, up to 40 percent of the total cost is expended on acquiring, delivering and handling concrete barriers. Additionally, concrete barriers have little or no ability to absorb shock upon impact, and have a high friction factor. This increases the damage to vehicles which collide with such barriers, and can lead to serious injuries to passengers of the vehicle.
In an effort to reduce weight, facilitate handling and shipment, and provide improved absorption of vehicle impact forces, highway barriers have been designed which are formed of a hollow plastic container filled with water, sand or other ballast material such as disclosed in U.S. Pat. Nos. 4,681,302; 4,773,629; 4,846,306, 5,123,773 and 5,882,140. For example, the '302 patent discloses a barrier comprising a housing having a top wall, bottom wall, opposed side walls and opposed end walls interconnected to form a hollow interior which is filled with water. The ends of each barrier couple to an adjacent barrier to form a continuous wall. The container structure is preferably formed of a resilient, plastic material which is deformable upon impact and capable of resuming its original shape after being struck. The container further includes longitudinally extending, spaced traction spoiler channels which are intended to reduce the area of potential impact, and thus the tendency of the vehicle to climb the walls of the barrier and vault over it into the opposing lane of traffic.
The '629, '306, '773 and '140 patents noted above represent further advances in deformable highway barrier designs. The first two patents disclose barriers which comprise a longitudinally extending housing made of semi-rigid plastic which is self-supporting, and has a predetermined shape which is maintained when filled with water, sand or other ballast material. Such devices are connected end-to-end by a key insertable within grooves formed in the end walls of adjacent barriers. Interconnected fill openings are provided which permit adjacent barriers to be filled with water or other ballast material when laid end-to-end.
The '773 and '140 patents disclose further improvements in barrier devices including side walls formed with higher curb reveals, a horizontally extending step and vertical indentations in order to assist in maintaining the structural integrity of the container, and internal baffles for dampening movement of water or other ballast material within the container interior. Interlocking male and female coupling elements are formed on the opposite end walls of each barrier to facilitate connection of adjacent barriers end-to-end. Additionally, channels or openings are formed in the barriers from one side wall to the other to permit the insertion of the tines of a fork lift truck therein for easy loading, unloading and handling of the barriers.
Despite improvements to highway barrier of the type described above above, some deficiencies nevertheless remain. One problem involves leakage of ballast material from the barrier interior. It has been found that defects can occur in the walls and in the joints between adjacent walls during the process of molding plastic barriers. Additionally, the plastic barriers can be relatively easily punctured on the job site by fork lift trucks or other equipment. Water is the most commonly used ballast material, and cracks or other defects in the barrier walls causes leakage which results, over time, in the complete drainage of water from the barrier. It is time consuming and inefficient to replace a leaking barrier along the length of the barrier wall, and repairs to individual barriers are inconvenient and expensive.
Another problem with highway barriers, both those formed of concrete and barriers having walls made of plastic material, relates to attenuation of the force of an impact with a moving vehicle. As noted above, concrete barriers have little or no ability to absorb or attenuate the force resulting from impact with a vehicle. If a vehicle grazes the concrete barrier at a shallow angle it essentially “bounces off” of the barrier and is turned back into traffic in the direction the vehicle was originally moving. Contact with a concrete barrier at a sharper angle can cause severe damage to the vehicle, and injury to its occupants, since the force of impact must be absorbed virtually entirely by the bumpers, side panels and other parts of the vehicle.
Highway barriers formed with plastic walls and filled with a ballast material such as water are more effective in absorbing the force of impact with a vehicle than concrete barriers. However, it has been found that the plastic material forming the barrier walls either breaks apart upon impact with a vehicle, or provides what can be characterized as a “rebound” effect. Instead of absorbing a vehicle impact so that the force is attenuated or transferred throughout the barrier device, the plastic material forming the barrier walls tends to deflect in the localized area of impact and then return or rebound to its original shape with the assistance of the ballast material in the hollow interior of the barrier device. Such rebound or return motion exhibited by the plastic walls exerts a force on the vehicle tending to stop or slow it down relatively quickly, or abruptly change the direction of movement of the vehicle, which, in turn, is transferred to the occupants of the vehicle.